Optical illusion art, also known as Op Art, uses patterns and visual tricks to create the illusion of movement, changing form and flashing and vibrating patterns. Pioneers of this style include Victor Vasarely, who is considered one of the founders of the movement. Another influential Op artist was Bridget Riley, whose 1961 work "Movement in Squares" uses grids of colored stripes in black and white that produce the optical effect of rippling movement when viewed.